Well if you just increased your speed In the direction you were already travelling then it's not your fault at all, don't feel bad.
I must say that I'm confused by the amount of people who are under the impression that a dog running in their direction is a sign that they are going to be attacked by the dog in question.
Ninety nine percent of dogs would never attack people. Many may bark and even sound aggressive, and chasing after things is just a game to them. Even though a bark may sound aggressive it's simply the only noise they can make and they bark that same way when they are happy.
It must be mostly people that have never lived with a dog that have an overreaction to dogs.
Dogs sense fear, they pick up mental signals that we don't even know we're projecting. If you are frightened of a dog then the dog will be more likely to be aggressive because it suspects you have bad intention.
I would be far more worried about coming across undesirable people on my rides.